U.S. Pat. Appl. No. 2008/0047964 (Denner et al, assigned to CO2PAC) discloses a container comprising a pressure panel located in the bottom portion of the container.
According to Denner, the pressure panel is movable between an outwardly-inclined position and an inwardly-inclined position to compensate for a change of pressure inside the container. In order to alleviate all or a portion of the vacuum forces within the container, the pressure panel is moved from the outwardly-inclined position by a mechanical pusher after the container has been capped and cooled, in order to force the pressure panel into the inwardly-inclined position.
Tests conducted on such a container showed that, once inverted to the inwardly-inclined position, the pressure panel does not maintain its position but tends to sink back under the pressure of the content. In the end, after the content has cooled, the container has lost much rigidity and therefore feels soft when held in hand. When stacking or palletizing the containers, there is a risk for the lower containers to bend under the weight of upper containers, and hence a risk for the whole pallet to collapse.